Overview

Comprehensive Description

Description of Elasmobranchii

The elasmobranchs, the skates and rays, together with the chimaeras make up the cartilaginous fish (they have no calcified bones). Also, unlike the bony fish, elasmobrachs have no swim bladders. Again, unlike bony fish with one gill cleft, these fish have five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth lie in several series. The upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate marine waters, a few occur in freshwaters. There are about 1000 species.
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Physical Description

Morphology

Sexual Dimorphism

Females generally larger, but males larger in some species; Sexual Dimorphism in shape (males thinner), head (males flatter), mouths and teeth; pelvic fins of males are modified as claspers for mating.
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Ecology

Associations

Known prey organisms

Elasmobranchii (elasmobranch fishes) preys on:
Bullia
Ovalipes

Based on studies in:
South Africa (Desert or dune)

This list may not be complete but is based on published studies.
  • A. C. Brown, Food relationships on the intertidal sandy beaches of the Cape Peninsula, S. Afr. J. Sci. 60:35-41, from p. 39 (1964).
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Swimming efficiently: sharks
 

Sharks are efficient swimmers in part due to their complex hydroskeleton.

         
  "It came as more of a surprise than it should have when Wainwright, Vosburgh, and Hebrank (1978) showed that sharks utilized a hydroskeleton. Sharks, after all, have conventional skeletons, albeit somewhat less calcified ones than that of most other vertebrates. Shark skin is sturdier stuff than fish skins generallyand it has the crossed helical fiber array typical of these hydrostatic arrangements, shown in figure 20.5b. The system, though, is more complex than those described previously--muscles attach directly to the skin, which thus acts both as external, pressure-resisting membrane and as an external, whole-body tendon. Fiber angles, not unreasonably, vary with location on the fish--the unstretchy skin must transmit the forces generated by the body musculature back toward the tail. During locomotion, the pressure inside the body of a shark rises to as much as 200 kilopascals--twice atmospheric and as high as that inside an automobile tire. So sharks are just shark-shaped balloons with teeth.

"In sharks, the peculiar resistance of crossed helical fibers to torsion may have functional significance, at least of a negative kind. Sharks lack swimbladders and thus sink if inactive. Swimming must produce a little lift in addition to thrust, and a shark gets that lift, in part, by beating a tail fin that extends farther dorsally than ventrally, as you can see in the figure. That asymmetry might make a shark uselessly twist lengthwise, reversing twist twice during each full tailbeat--were it not for a torso that, while flexible in bending, resists twisting." (Vogel 2003:415-416)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
  • Wainwright, SA; Vosburgh, F; Hebrank, JH. 1978. Shark skin: function in locomotion. Science. 202(4369): 747-749.
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Functional adaptation

Scales protect skin: cartilaginous fish
 

The skin of cartilaginous fish is protected by a covering of abrasive placoid scales, called denticles.

     
  "The other main type of fish scales are those known as placoid scales or, more commonly and appropriately, denticles: 'little teeth' (diagram d). They are found on the primitive cartilaginous fishes, sharks, skates, and rays (whose skeletons are made of cartilage, not bone). Each denticle grows up from the dermis until its curved tip breaks the skin surface -- denticles are not covered with skin as bony scales are. Each denticle, like a human tooth, is made of dentine (tooth ivory) capped with enamel; each has a pulp cavity containing nerves and blood vessels. Denticles are usually small, but may be sharp. Brushing against the skin of a shark, can flay the skin of a swimming man like a particularly vicious sandpaper." (Foy and Oxford Scientific Films 1982:91)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records:21867
Specimens with Sequences:16537
Specimens with Barcodes:11900
Species:1087
Species With Barcodes:987
Public Records:9084
Public Species:549
Public BINs:593
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Barcode data

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